U-value: A measure of air-to-heat transmission (loss or gain) through a window due to the thermal conductance and the difference in indoor and outdoor temperatures. As the U-value decreases, so does the amount of heat that is transferred through the glazing material. The lower the U-value, the more restrictive the fenestration product is to heat transfer. Reciprocal of R-value.
UL (Underwriters Laboratories): A private research firm located in the United States that tests, classifies and determines the safety of household products, especially electrical appliances and electronic devices.
ultraviolet (UV) degradation: A reduction in certain performance limits caused by exposure to ultraviolet light.
ultraviolet rays (UV rays): The invisible rays of the light spectrum that are at its violet end.
undercoat: A coating applied prior to the finishing or top coats of a paint job. It may be the first of two of three coats. Also called a priming coat.
undercounter: A style of lavatory that is positioned under the cutout of the countertop.
underground plumbing: The plumbing drain and waste lines that are installed beneath a basement floor.
underlayment: A material placed under finish coverings, such as flooring or shingles, that provides a smooth, even surface for applying the finish.
union: A plumbing fitting that joins pipes end-to-end so that they can be dismantled.
union nut: A fitting that joins two sections of pipe.
unsafe: A condition of an area, system, component or procedure that is judged to be a significant risk of injury to people during normal use. The risk may be due to damage, deterioration, improper installation, or a change in accepted construction standards.
Uo Value Zone: The Uo Value Zone is determined from a thermal zone map. The Uo value is the overall coefficient of heat transmission of the manufactured home based on the respective thermal zone location and an indoor design temperature of 70º F, and is defined in units of BTU/(hour)(square foot)(º F). The overall Uo value for the home thermal envelope design must not exceed the values as defined by the thermal zone map. The design Uo value for Thermal Zone 1 is 0.116 BTU/hr x ft2 x º F; for Thermal Zone 2 is 0.096 BTU/hr x ft2 x º F; and for Thermal Zone 3 is 0.079 BTU/hr x ft2 x º F.
uprights: Vertical members that support the sides of a trench to prevent its collapse.
utility easement: The area of the earth that holds electrical, gas or telephone lines. These areas may be owned by the homeowner, but the utility company has the legal right to enter the area as necessary to repair and service the lines.
UV rays: Ultraviolet rays from the sun.